Exterior surfaces, primarily wood siding, require repainting periodically to maintain appearance and protection of the substrate. Adhesion of newly applied paints to weathered surfaces, however, can be poor due to a weathered surface exhibiting a chalking condition. Chalking can occur after extended exposure to the weather due to deterioration of the old paint film which causes unprotected or dry unbound pigment particles to appear on the substrate surface.
Solvent based paints provide good adhesion to chalking surfaces since the organic solvent and binder can penetrate and wet the chalky surface. Latex paints, however, do not provide penetration or desired wetting of chalky surfaces regardless whether the polymeric binder type is acrylic, vinyl-acrylic, styrene acrylic or the like. If an alkyd is blended with latex binder, the chalk adhesion can be improved but other problems occur. For instance, the alkyd diminishes latex polymer properties and causes undesirable oxidative degradation thereby reducing the useful life of the paint film. Combinations of polymers, including aqueous dispersed polymers mixed with organic dispersed polymers are shown in U.S. Pat. No. 4,504,609, U.S. Pat. No. 4,529,765, U.S. Pat. No. 4,199,400, and U.S. Pat. No. 3,454,516. Similarly, U.S. Pat. No. 4,722,965 discloses a blend of emulsion polymers based on an adhesion promoting latex containing copolymerized amino-acrylate (WAM) monomer.
It now has been found that an emulsion latex binder copolymer containing minor amounts of copolymerized fatty acid acrylate or methacrylate such as lauryl or stearyl methacrylate provides the necessary chalk adhesion of the latex binder without the need for extraneous organic adhesion additives thereby eliminating the need for alkyd or other detracting adhesion additives. Thus, external adhesion promoters can be eliminated. These and other advantages of this invention will become more apparent by referring to the detailed description and illustrative examples.